On Mon, 31 Jan 2022 17:42:38 +0100 Erik Kaashoek <e...@kaashoek.com> wrote:
> he clock is a 200MHz perfect clock. > The events come from an unknown quality XCO at 10 MHz > The measurement interval is 0.1 seconds > The goal is to derive the phase (and also the frequency) of the XCO versus > the clock from the counter data in the highest possible accuracy. Once this > is done the rest of the post processing of multiple measurements can be > done in tools like Timelab. Ok, you seem to have fallen into the beginner's trap of frequency measurement. You are trying to measure frequency using many samples and then taking the average of this. Unfortunately, unless you are using very stable oscillators and only short periods of total measurement time, your average will get worse the more samples you collect instead of getting better (i.e. your avarege will fluctuate more and more the more samples you take instead of converging to a certain value). This is the curse of 1/f^a noise (aka flicker noise) limited measurements. It also goes as non-convergence of noise in clocks (or generally metrological measurments). Assuming ideal oscillators does not help either. Your oscillators aren't ideal. Not at the time scales you are looking at. The only way to make them ideal in this sense and have the measurement converge is to couple both oscillators through some sort of PLL. But then, you wouldn't need to measure their relative frequencies, you would already know it. I suggest you to read at the very least IEEE 1139[1], NIST TN 1337[2] and NIST SP 1065[3] Attila Kinali [1] IEEE Standard 1139 "Definition of physical quantities for fundamental frequency and time metrology" [2] "Characterization of Clocks and Oscillators" NIST Technical Note 1337, by Sullivan, Allan, Howe and Walls, 1990 http://tf.nist.gov/general/pdf/868.pdf [3] "Handbook of Frequency Stability Analysis", NIST Special Publication 1065, by W.J. Riley, 2008 http://tf.nist.gov/timefreq/general/pdf/2220.pdf -- In science if you know what you are doing you should not be doing it. In engineering if you do not know what you are doing you should not be doing it. -- Richard W. Hamming, The Art of Doing Science and Engineering _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.